1. Field of the Invention
The present invention relates to hearing aids. The invention further relates to a hearing aid comprising a battery compartment prepared for receiving a battery, where two contacts are arranged to draw an electrical current from an inserted battery in order to power electrical parts of the hearing aid.
A hearing aid, constructed to be carried behind the ear or within the ear, is made as small as possible for the convenience of the hearing aid user.
The compartment for the battery and the spring loaded battery contacts for establishing electrical contact to the battery take up a significant space in the hearing aid. The battery itself and the battery contacts often define the minimum possible thickness of the hearing aid.
At the same time it is important to ensure a good electrical contact between the battery surface and the contact points in order to be able to draw a sufficient electrical current to the electronics of the hearing aid, and to avoid or minimize any power loss in the transition from battery to contact point. For this purpose the point of contact should be pressed against the battery with sufficient load to get through any layer of dirt, such as grease and oxide, on the surface of the battery.
The battery compartment and spring loaded contacts must be adapted for frequent change of battery, e.g. one to two times a week. This implies that especially the contacts and the spring must be made sufficiently reliable and durable to resist this frequent handling.
2. The Prior Art
In order to provide a high load on the point of contact by a traditional hearing aid battery spring, the distance which the spring will have to be moved during insertion of a battery becomes relatively long. This will make the design of the battery compartment and the spring more complicated, or the battery insertion will be more difficult. Also, the battery springs should preferably weigh as little as possible, meaning that the material should not be made thicker than necessary.
One problem in the known spring loaded battery contacts is that it is not possible to achieve a high load of the battery contact point against the battery surface with a spring moving only a short distance, and at the same time provide a simple design comprising only few parts to assemble during manufacturing.
The tolerance on the dimensions of batteries used for hearing aids is relatively large. As an example the standard IEC 60086-2 (edition 12.0) mentions that a battery designated PR41 (which is a standard hearing aid battery) can have a thickness, or height, in the range from a minimum of 3.30 mm to a maximum of 3.60 mm. Further to this, the typical zinc-air batteries used for hearing aids have a tendency of swelling during discharging. The standard IEC 60086-1 mentions that an increase in battery thickness of 0.25 mm is allowable. Thus a battery spring in this example must be able to provide a sufficient load through the point of contact to a battery varying in thickness from 3.30 mm to 3.85 mm.